1. Technical Field
This invention relates to apparatus and method for testing the sealing effectiveness of dynamic seals, and particularly dust-exclusion seals operating in a dust-laden environment.
2. Related Prior Art
Dynamic seals are used in many engine and machine applications to seal between relatively movable parts. Dynamic oil seals are used to close the annular gap between the crankshaft of an engine and the opening in the block through which the crankshaft extends. Such seals include at least one oil lip to retain lubricant, such as oil or grease, on one side of the seal and include one or more dust lips of the radial or face type to exclude contaminants such as dust and dirt on the opposite atmospheric or air side of the seal.
Various test apparatus and procedures have been proposed and/or are in use in connection with dynamic oil seals to test their effectiveness for particular applications. U.S. Pat. No. 3,987,663, for example, discloses a non-destructive test apparatus for quickly testing the integrity of seals in a production setting. The seals are mounted on a fixture and pressurized with air on one side and monitored on the opposite side for air leakage which would indicate seal failure. The disclosure of the above patent is incorporated herein by reference. While such a test method and apparatus is beneficial for quickly testing seals in a production setting, it is desirable during the development and qualification of dynamic seals to test their effectiveness under conditions which simulate or exaggerate the actual operating conditions which they would likely be subjected to in service.
Many such oil seals are designed to operate industry environment and thus, in addition to the primary lubricant sealing lip, include one or more of the radial or face-type dust lips which operate to exclude dust from entering the seal and contaminating the oil lip. Oil lips are commonly made from low friction flouropolymer materials, such as PTFE. It is well known that such materials perform well only when properly protected. Dry dust-laden conditions quickly degrade PTFE oil lips leading to early seal failure. For this reason, dust lips are often fabricated of materials which tolerate operating in a dry, dusty environment more so than the oil lip.
The traditional approach to testing the effectiveness of such seals operating under dust-laden conditions has been to mount the seals in a housing about a rotating shaft. Oil is maintained on the oil side of the seal as it would be during normal use, and a dust chamber is provided on the opposite side of the seal to expose the dust lip to a dust-laden environment. Housed within the dust chamber is a single mixer blade mounted on an extension of the test shaft. The blade rotates at high speed with the shaft and collects and disburses the dust within the chamber. Over time, it has been observed that the high speed of the blade tends to pack the dust against the wall, forming a trench in the accumulation of dust at the bottom of the chamber in which the blade runs, providing less than the optimum amount of dust available for dispersion within the chamber by the blade. Difficulties are thus encountered in maintaining a uniform dust cloud environment within the chamber over the duration of the test. The seal is operated until oil is observed leaking past the dust lip. Such indicates a failure of the oil lip, likely accounted for by an earlier failure of the dust lip in excluding dust from contaminating the oil lip.
One drawback to such a test is that it does not provide much information about why a test seal may have failed. It would be beneficial to know, for example, when and how much dust passes by the dust lip over the course of the test period and to examine the seal at the conclusion of the test for evidence of dust patterns or accumulations which could aid in the evaluation of the seal and provide information helpful in altering the design of the seal, if necessary, to further improve performance. With current testing techniques, however, the presence of the oil on the oil side of the seal precludes the gathering of such information. Some of the dust which escapes past the dust lip passes through the oil lip and into the oil, making its collection highly impractical. Upon oil lip failure, the oil which leaks past the damaged oil lip wets the remaining dust present between the oil and dust lips, washing away at least some of the dust and disturbing the dust patterns and/or accumulations that may have been present that could be helpful in analyzing the performance of the dust lip.
It would thus be desirable to have a test apparatus and procedure for testing the performance of dynamic lip seals operating in a dust-laden environment which would enable collection and analysis of the dust which passes by the dust lip to provide more information about the performance of the dust lip operating under such conditions. Such is provided by the present invention.